Animals that estivate include snails, crocodiles, hedgehogs, tortoises, birds and lungfish. Estivation is the process by which animals enter a state of dormancy during hot times of year to conserve energy. In order to estivate, animals find places that are cooler than the surrounding air, such as underground burrows or holes in tree trunks. Hot and dry conditions, not a lack of food, usually cause animals to estivate.
Snails achieve a state of dormancy during the summer in tree trunks, under leaves or on stone walls. The snail retreats completely into its shell until weather conditions improve. When snails estivate on the ground, mucus seals the shell except for one small opening to let air into the snail's shelter.
Crocodiles go into suspended animation during severe droughts and prey is scarce. Lungfish estivate for periods up to three years without water. Lungfish bury themselves in mud and then cover their bodies in mucus to hold in moisture. Lungfish breathe using lungs instead of gills and get oxygen through a mucous tube to the surface.
Estivation most commonly occurs in desert and tropical biomes where temperatures can reach extreme levels for long periods. Animals enter estivation by lowering their heart, breathing and metabolic rates to conserve energy.